LU-16498 obdclass: fix write unlock for internal case

LU-16498 obdclass: fix write unlock for internal case

Holding a (write) lock is mandatory for put_entry(), so fix that in
refresh_entry_internal().

Fixes: 127128bed3 ("LU-16498 obdclass: change uc_lock to rwlock")
Test-Parameters: kerberos=true testlist=sanity-krb5
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: If55182ca29f37f2a783fdb88ba46512944a61c47
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53674
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>